Impact Proxies from Europe Postdate Laacher See Eruption, Mark Younger Dryas Onset, and May Relate to Hiawatha Crater in Greenland
Abstrakt
The Younger Dryas (YD) climate episode (about 12,850-11,650 calendar years before present [cal BP]) is an event recorded widely across the Northern Hemisphere. We conducted multiple analyses at high resolution of a YD-age sedimentary sequence from Stara Jimka, a paleolake in the Bohemian Forest, Czech Republic. Age-depth modeling indicates that, in our record, a central European warming trend was interrupted at about 13,020+/-110 cal BP by the sudden onset of cooling (120 y) known as the Gerzensee climate oscillation and marked by the deposition of fine-grained sediment at this location. That cooling episode ended at about 13,001+/-66 cal BP and was followed by a about 120-y-long warming trend. After that, the Laacher See tephra depositional event, dating to about 12,820+/-20 cal BP, continued an overall warming trend. The composition of the Laacher See volcanic tephra in this section likely corresponds to the middle eruption sequence. Finally, the deposition of glassy microspherules marks the onset of the YD climate change at about 12,755+/-92 cal BP. The sequence across the YD onset is marked by (1) a peak in glassy microspherules (117,000/kg), (2) a peak in framboidal spherules (14,000/kg), (3) significant changes in the lake's weathering proxies, and (4) major changes in local fauna (cladocerans, chironomids) and flora (pollen record, fire regime), showing a shift to unfavorable environmental conditions (decrease in temperature and lake trophy status). Collectively, this evidence is consistent with the co-called YD impact hypothesis and evidence of one or more cosmic airburst events occurring at this time. We have analyzed the radar ice record and both gravity and magnetic data over the Hiawatha crater in northwest Greenland and found not only that the impact was likely directed southward, but also that this impact could be the source of iron rich microspherules observed in the lake sediments in Czechia 12750 cal years BP.